When Caprica was initially planned, the series was set 50 years before the Fall of the Colonies. The timeline was subsequently readjusted from 50 to 58 years before the Fall. However, it was later realized this would have made Willie too old to be Admiral Adama in Battlestar Galactica. He would have been in his 70s instead of his 60s. So they killed Willie and Bill Adama was born so he would be the appropriate age to play the Admiral.